The present invention relates to plasma-enhanced chemical vapor deposition (PECVD) of materials such as silicon nitride, silicon oxide and silicon oxynitride; to the use of parallel plate PECVD reactors for depositing these materials; and, in particular, to a gas inlet manifold for a parallel plate reactor and a method of using the manifold and the reactor for depositing these materials at a high rate and for depositing silicon nitride and silicon oxynitride without using high-hydrogen content gases such as ammonia.